Color filters used in an image sensor can include a transparent film formed under or on the surface of the color filter to improve flatness and to protect the color filter. The transparent film must be optically transparent in the visible region, have high film strength and exhibit sufficient heat and chemical resistance to withstand subsequent processes such as heating, cleaning, development and etching after forming the transparent film. In particular, an underlying transparent film of a color filter for an image sensor should be capable of suppressing the reflection of UV rays which are irradiated to pattern a color resist, to thereby prevent the occurrence of pattern defects in the color filter by various adverse factors such as halation and standing waves.
Japanese Patent Publications Nos. Hei 1-134306, Sho 62-163016 and Sho 63-131103 disclose compositions for transparent films for color filters comprising glycidyl methacrylate, polyimide and a mixture of a melamine resin and an epoxy resin as the primary components, respectively.
Epoxy resin compositions can be used to produce protective films for color filters having reliable adhesive strength, heat resistance, chemical resistance and water resistance. For instance, Japanese Patent Publication No. Hei 08-050289 teaches a curable resin composition comprising a glycidyl methacrylate polymer and a phenolic curing agent. Further, Japanese Patent Publication No. Hei 08-201617 teaches a resin composition for a transparent film comprising an epoxy resin, a curing agent and an organic solvent wherein the curing agent is a reaction product of a styrene-maleic anhydride copolymer and an amine.
Generally epoxy resins are mixed with curing agents (so-called “two-part compositions”) immediately before use due to their rapid reaction with the curing agents. It is known that epoxy resins are unsuitable for use in the preparation of one-part compositions. Two-part compositions, however, are complicated to handle and unsuitable for industrial-scale preparation.
None of the aforementioned prior art techniques discloses one-part compositions comprising an epoxy resin while simultaneously satisfying the requirements for transparency, film strength, heat resistance, acid resistance and alkali resistance. Further, a transparent film for a color filter capable of absorbing UV light has not yet been developed.